Hydrogen peroxide controls transcriptional responses of ERF73/HRE1 and ADH1 via modulation of ethylene signaling during hypoxic stress.

Hypoxia, or oxygen deficiency, is an abiotic stress that plants are subjected to during soil flooding. Therefore, plants have evolved adaptive mechanisms to sense oxygen deficiency and make coordinated changes at the transcriptional level. The results of this study show that the interplay between hydrogen peroxide and ethylene affected the transcriptional responses of ERF73/HRE1 and ADH1 during hypoxia signaling. H₂O₂ affected the abundance of ERF73/HRE1 and ADH1 mRNAs in both wild-type Arabidopsis and the ethylene-insensitive mutant, ein2-5. Promoter analysis was conducted using transgenic plants expressing an ERF73/HRE1 promoter-β-glucuronidase reporter gene construct. GUS staining observations and activity assays showed that GUS was regulated similarly to, and showed a similar accumulation pattern as, H₂O₂ during hypoxia. The transcript levels of ERF73/HRE1 and ADH1 were significantly decreased in the WT by combined hypoxia and diphenylene iodonium chloride (DPI, an NADPH oxidase inhibitor) treatment. In ein2-5, induction of ERF73/HRE1 was also reduced significantly by the combined hypoxia and DPI treatment. In contrast, ADH1 mRNA levels only slightly decreased after this treatment. When DPI was supplied at different time points during hypoxia treatment, H₂O₂ had critical effects on regulating the transcript levels of ERF73/HRE1 and ADH1 during the early stages of hypoxia signaling. The induction of hypoxia-inducible genes encoding peroxidases and cytochrome P450s was affected, and accumulation of H₂O₂ was reduced, in ein2-5 during hypoxic stress. Together, these results demonstrate that H₂O₂ plays an important role during primary hypoxia signaling to control the transcriptional responses of ERF73/HRE1 and ADH1 via modulation of ethylene signaling.